A month-old ring tailed lemur, left, receives a lick from it's one-year-old sister "Safina," right, in an exhibit at the Franklin Park Zoo, in Boston, Wednesday, April 27, 2011.

A month-old baby lemur, right, rides on her seven-year-old mother's back in an exhibit at the Franklin Park Zoo, in Boston, Wednesday, April 27, 2011.

Nebbie, a seven-year-old ring tailed lemur, left, carries her month-old baby on her back in an exhibit at the Franklin Park Zoo, in Boston, Wednesday, April 27, 2011. Nebbie gave birth to twins on March 31, 2011, but the baby primates have yet to receive names or have their sex determined. Lemurs, endemic to Madagascar, are social animals and live in female dominated groups in the wild.